Control of a modern electric power plant is a complex process. At the most general level, such a plant comprises a generator coupled to a turbine or other source of mechanical power, a circuit breaker for connecting the generator to a bus, and a transformer for connecting the bus to a power grid. In a hydroelectric plant, a turbine converts the energy of moving water to rotation of the generator. The control system for an electric power plant must be capable of managing a large assembly of devices and instruments in real time. For example, the control system must regulate the generator field to regulate voltage or power, control the circuit breaker such that it opens and closes at appropriate times, and monitor and control all relevant turbine parameters such that the generator can produce the appropriate frequency output when the plant is being starting up or reconnected to the grid, or the appropriate energy level once the plant is connected to the grid.
In the past, the most typical approach to control systems for electric power plants has been to instal a large number of sensors, relays, and dedicated control systems for controlling particular aspects of plant operation. For example, in a hydroelectric plant, a control system will be provided for sensing turbine speed and generator voltage and for responsively regulating the water flow in accordance with predefined criteria. A typical power plant thus includes a large number of separate instruments, many of which were installed at different times and produced by different manufacturers. Typical instruments found in a present day power plant include transducers for voltage, amperage, VARs, watts, watt hours, frequency and power factor, meters for displaying measured values of all of the above parameters, relays for controlling the governor, the display of alarms, the start and stop functions, automatic synchronizing functions and so forth, plus a large number of protective relays scattered throughout the plant. Information is typically reported to an operator via an annunciator panel that consists of a grid of transparent displays that can be selectively illuminated. A traditional way of keeping records in a power plant is a log sheet, i.e., a clipboard that must be filled out with metering data at frequent intervals. Some power plants have chart recorders for stator and bearing temperatures, and separate chart recorders for automating the log sheet function.
In view of the above, it is clear that there is a need for an integrated control system for operating electric power plants. However development of such a control system is a difficult task. An integrated control system must be cost effective, must be reliable and fail-safe under all conditions, and must be readily adaptable to each particular power plant in which it is installed. Because virtually no two power plants are alike, it is this latter requirement in particular that has to date prevented the development of an effective, integrated power plant control system. In particular, although control systems for individual power plants have been designed and installed, such control systems in the past have been one of a kind adaptions to a particular power plant configuration.